1. Field of the Invention
The present invention relates to a structure of direct type backlight module with high uniform emitting light, which emphasizes on a direct type backlight module with high efficiency of light diffusion and transmission and low-cost diffusing plate.
2. Description of the Related Art
With the increment of HDTV, DVD player and Digital TV requirement, consumers are more and more concerned about the image quality of television. Besides, some defects of conventional CRT TV are high power consumption, high radiation, blinking, and heavy weight. Therefore, new generation display device having high solution in different monitors competition during these years has gradually placed CRT. Liquid crystal display with potential display technology has been always highly concerned for new generation display. The manufacturers in Japan, Taiwan and Korean are devoted into LCD technology research and adopting large-scale production equipment, therefore, the quality of LCD has been continuously improved and marketing price is getting down which bring the requirement of LCD and more criteria on related technology. The image of liquid crystal monitor is controlled by electric fields power, but liquid crystal panel itself can not emit light and provides monitor light through backlight module. Generally speaking, LCD has two different kinds of backlight source that are side type and direct type. Side type backlight source cannot provide high brightness and uniform light on the application of large-size liquid crystal monitors, due to being influenced by lamp tubes and light transmission distance. On the contrary, direct type backlight can achieve the criteria of large-size liquid crystal monitor through increasing lamp tubes and diffusion device design. Besides, light guide plate of side type backlight module will increase thickness while size is enlarged to achieve uniform distribution of light. According to the calculation, the weight of light guide plate whose average brightness 5000 cd/m2 for 21″ is over 2 kilogram. The trend of present monitor is towards to light weight, the weight of light guide plate becomes a significant criterion. Using light diffusing plate can reduce in a range of from 60 to 80% weight that has obvious advantage for the application of large-size backlight module.
Light diffusing plate of direct type backlight module replacing light guide plate of side type is an important component to have scattering and uniformity light. The primary function of “Light diffusing plate” is to scatter light, such as light box, light signboard, even the light box which using for X-ray examination in the hospital, that all use the similar diffusing plate to scatter the light uniformly. That causes in good effect on light scattering. Although the diffusion efficiency of early diffusing plate fits the requirement, the light transmission ratio and uniformity are still not good for display application, whose defect is the insufficient brightness. Generally speaking, the transmission rate of the whole light field of these diffusing plates are in a range of from 30 to 50% that has already not satisfied the consumer's requirement, under the trend of high brightness of display. Japanese diffusing plate manufacturers devote to solve these defects recently, by adding different categories of light dispersant and strictly controlling the process, the light transmission efficiency and uniformity has been successfully improved. Although transmission rate has increased in a range of from 50 to 70%, the transmission rate is not satisfied by the customers as high criteria product. On the other hand, in order to achieve the design of thinner monitor product, backlight module has to develop towards to lightweight and thin, therefore, the higher diffusion efficiency is required. But much light diffusion dispersant has been used for diffusing plate and causes in reducing transmission rate. In brief, high diffusion and transmission rate for the present diffusing plate are hardly presented at the same time. There is only way to satisfy the requirements of high brightness and diffusion is to modify the structure of diffusing plate or backlight module. The manufacturers of LCD TV or backlight module adopt a method that is to use a diffusing plate with higher transmission rate. The vestige of CCFL can not be uniformed by diffusing plate, therefore, 1 to 2 diffuser put at the emitting facet of diffusing plate to achieve the effect of light scattering again which resulted in a range of from 5 to 10% light energy loss, then accommodating to prism sheet to bring light and counterbalance the loss. Finally, the purpose of thin and lightweight backlight module can be implemented but resulted in huge increment of cost and lessening the visible angle of TV.
Liquid Crystal Display itself cannot emit light and requires backlight module to provide light source for monitor. Diffusing plate is an important component of backlight module for light scattering. The function of diffusing plate is to scatter light uniformly emitting from CCFL to provide stable and uniform light source for liquid crystal panel. Moreover, the brightness and quality of LCD are very related to the efficiency of light source. In order to increase the effect of light scattering, the light dispersant is added into said diffusing plate, but the price of light dispersant is very expensive.
Therefore, to propose a structure of direct type backlight module with high uniform emitting light, according to the aforementioned problems, which enable to solve the defects of using much, light dispersant for diffusing plate and to increase light diffusion and transmission and cost effectively. Based on the inventor engaging on the research and develop and sales experiences for the related products for many years, the inventor finally proposes a method to solve the aforementioned problems for a structure of direct type backlight module with high uniform emitting light.